ERROR: Cannot read directony on FTP server

[Liu.]

Hello,

Local machine：FFS 13.9, Windows server 2019
FTP server: FileZilla Server 1.9.4, Windows 10
Copying from local folder to FTP server
Number of files operated：over 13000
Number of folders: over 300

I am getting errors: Cannot read directony "ftp://name@xx.xx.x.x/Backup/xx/xx". CURLE RECV ERROR: Recv failure: Connection was reset [curl easy_perform].
Most directonys are read successfully, only some of them read failure. these errors occur every time when i synchronize, but everytime the directonys read failed are deffient.

if i resuce the number of files, such as 6000 files, 27 folders, these errors will not show again.
if i turn off firewall on FTP server, these errors will not show again.

Does anyone know how can i solve this problem?

Thanks!

[Liu.]

This error only occurs in tls mode. In plain mode, there is no error any more.